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====Monitoring====
Oracle database management tracks its [[computer data storage]] with the help of information stored in the <code>SYSTEM</code> tablespace. The <code>SYSTEM</code> tablespace contains the [[data dictionary]]—and often (by default) [[index (database)|indexes]] and [[cluster (computing)|clusters]]. A data dictionary consists of a special collection of [[table (database)|tables]] that contains information about all user-[[object (computer science)|objects]] in the database. Since version 8''i'', the Oracle RDBMS also supports "locally managed" tablespaces that store space management information in bitmaps in their own [[header (computing)|headers]] rather than in the <code>SYSTEM</code> tablespace (as happens with the default "dictionary-managed" tablespaces). Version 10''g'' and later introduced the <code>SYSAUX</code> tablespace, which contains some of the tables formerly stored in the <code>SYSTEM</code> tablespace, along with objects for other tools such as [[Oracle Enterprise Manager|OEM]], which previously required its own tablespace.<ref>{{cite book|last=Alapati|first=Sam R.|title=OCP Oracle Database 10g: New Features for Administrators Exam Guide|year=2004|publisher=McGraw-Hill/Osborne|isbn=0-07-225862-4|page=18|page=287}}</ref>
==== Disk files ====
{{Expand section|date=September 2009}}
Disk files primarily represent one of the following structures:
* Data and index files: These files provide the physical storage of data, which can consist of the data-dictionary data (associated to the tablespace SYSTEM), user data, or index data. These files can be managed manually or managed by Oracle itself ("Oracle-managed files"). Note that a datafile has to belong to exactly one tablespace, whereas a tablespace can consist of multiple datafiles.
* Redo log files, consisting of all changes to the database, used to recover from an instance failure. Note that often a database will store these files multiple times, for extra security in case of disk failure. The identical redo log files are said to belong to the same group.
* Undo files: These special datafiles, which can only contain undo information, aid in recovery, rollbacks, and read-consistency.
* Archive log files: These files, copies of the redo log files, are usually stored at different locations. They are necessary (for example) when applying changes to a standby database, or when performing recovery after a media failure. It is possible to archive to multiple locations.
* Tempfiles: These special datafiles serve exclusively for temporary storage data (used for example for large sorts or for global temporary tables)
* Control file, necessary for database startup. "A binary file that records the physical structure of a database and contains the names and locations of redo log files, the time stamp of the database creation, the current log sequence number, checkpoint information, and so on."<ref>Oracle Corporation, Oracle Database Concepts 11g Release 1 (11.2), http://download.oracle.com/docs/cd/E11882_01/server.112/e25789/glossary.htm#CHDDFGEC, 2011</ref>
At the physical level, [[data file]]s comprise one or more [[block (data storage)|data blocks]], where the [[block (data storage)|block size]] can vary between data files.
Data files can occupy pre-allocated space in the file system of a computer server, utilize raw disk directly, or exist within [[Automatic Storage Management|ASM]] logical volumes.<ref>
{{cite web | first = Bob | last = Watkins | authorlink = | title = Look inside ASM disk groups with Oracle 10''g''R2's ASMCMD
| url = http://articles.techrepublic.com.com/5100-10878_11-6154262.html | archiveurl = | work = techrepublic.com | publisher = ZDNet | ___location = | doi = | date = 30 January 2007 | archivedate = | accessdate = 2009-07-30
| quote = In 10''g'', Oracle introduced a new kind of storage for its database product. Automatic Storage Management (ASM) is a logical volume manager that takes physical disk partitions and manages their contents [...] Until ASM, there were only two choices: file system storage and raw disk storage.
}}
</ref>
===Database schema===
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